Image quality in CT scans of the heart may be affected by heart motion. Motion of the heart within the duration of a cardiac CT scan capture may result in the presence of motion artifacts in images derived from the cardiac CT scan.
FIG. 1 shows an image derived from a CT scan of the heart. Ellipses 2 indicate vessels with severe motion artifacts. Normally, in an image derived from a scan without significant motion artifacts, it may be expected that vessels would appear as approximately circular. However in FIG. 1 the vessels within ellipses 2 are significantly distorted.
Heart motion may particularly affect image quality in scans that are taken at high heart rates, for example heart rates over 60 beats per minute (bpm). Advanced scanners may obtain good image quality with moderately high heart rates, but may still see decreased quality at higher heart rates.
The range of patients for whom good quality cardiac CT scans may be obtained may in some circumstances be limited to patients who do not have high heart rates during the cardiac CT scan. For some patients, drugs such as beta-blockers may be administered to slow the patient's heart rate, for example to slow the patient's heart rate below 60 beats per minute. However, some patients may be unable to take beta-blockers, for example due to medical conditions. If good image quality at higher heart rates could be obtained, the number of patients who could benefit from good quality cardiac CT scans may be increased.
Some existing methods attempt to improve the quality of cardiac scans by capturing data over more than one heart beat. However, capturing data over more than one heart beat may increase the length of the CT scan and increase the radiation dose to the patient.
It is known to estimate heart motion by comparing scan data that is representative of different points in time, to determine the motion that has occurred between the different time points.